Various types of batteries have been developed heretofore, and in every battery, a packaging material is an essential member for sealing battery elements such as an electrode and an electrolyte. Metallic packaging materials have been often used heretofore as battery packagings.
On the other hand, in recent years, batteries have been required to be diversified in shape and to be thinned and lightened with improvement of performance of electric cars, hybrid electric cars, personal computers, cameras, mobile phones and so on. However, metallic battery packaging materials that have often been heretofore used have the disadvantage that it is difficult to keep up with diversification in shape, and there is a limit on weight reduction.
Thus, in recent years, there has been proposed a film-shaped laminate with a base material, a metal layer and a sealant layer laminated in this order has been proposed as a battery packaging material which is easily processed into diversified shapes and is capable of achieving thickness reduction and weight reduction. However, such a film-shaped packaging material is thinner as compared to a metallic packaging material, and has the disadvantage that pinholes and cracks are easily generated during molding. If pinholes and cracks are generated in a battery packaging material, an electrolytic solution may permeate to a metal layer to form a metal precipitate, resulting in generation of a short-circuit, and therefore it is absolutely necessary that a film-shaped battery packaging material have a property that makes it hard to generate pinholes during molding, i.e. excellent moldability.
Particularly, in recent years, a battery packaging material has been desired to have a further reduced thickness and weight, and layers that form the battery packaging material after molding have been required to have a further reduced thickness. However, when the thickness of a metal layer decreases to, for example, less than 30 μm, pinholes and cracks are very easily generated in the metal layer during molding of a battery packaging material.
Various studies have been conducted heretofore with attention paid to an adhesive layer for bonding a metal layer in order to improve the moldability of a film-shaped battery packaging material. For example, Patent Document 1 discloses that in a laminated packaging material which includes an inner layer including a resin film; a first adhesive agent layer; a metal layer; a second adhesive agent layer; and an outer layer including a resin film, at least one of the first adhesive agent layer and the second adhesive agent layer is formed of an adhesive agent composition containing a resin having an active hydrogen group on the side chain, a polyfunctional isocyanate and a polyfunctional amine compound to give a packaging material having high reliability in deeper molding.
As represented by Patent Document 1, many studies have been conducted heretofore on techniques for improving moldability with attention paid to blended components of an adhesive layer for bonding a metal layer and another layer in a battery packaging material including a film-shaped laminate, but there have been reported very few techniques for improving moldability with attention paid to the shape etc. of a metal layer after molding.